The present invention broadly relates to the detection of marking elements in a stack of substantially flat products and, more specifically, pertains to a new and improved method of, and apparatus for, detecting the position of a marking or separating element in a stack of substantially flat products, particularly labels.
Generally speaking, in the practice of the invention for detecting or locating a marking or separating element in a stack of labels, there is provided a detector or sensor arrangement, preferably a photodetector arrangement.
A machine or apparatus for fabricating labels and the like is known, for example, from Swiss Patent No. 657,338, published Aug. 29, 1986. In the machine disclosed therein, a stack of labels and transparent marking foils arranged therebetween are moved stepwise past a fixed or stationary light barrier. Whenever a transparent marking foil travels past the light barrier, the latter triggers the application of an ejector element which pushes to a certain extent the transparent marking foil out of the stack of labels. By virtue of the protruding marking foil, there is activated a parting or detaching element which dips into the stack of labels along the front or downstream side of the respective transparent marking foil, the parting or detaching element thereby parting the stack portion located in front of it.
The problem existing with this label fabricating machine or apparatus known to the art resides in the fact that the light barrier as well as the ejector element are fixedly arranged, while the stack of labels with the marking foils therebetween travels past at a feed speed determined by the cutting stroke of the stamping device. It is thereby readily conceivable that operational reliability decreases when the feed speed of the stack increases. On the other hand, limited feed speed results in a further drawback in that it is difficult to shorten the production time per label package. The output is therefore undesirably low.